System and method for recycling sterilant gas

ABSTRACT

A system for recovery and reutilization of sterilant gas mixture from a sterilizer chamber includes a storage tank in gaseous communication with a sterilizer chamber via a gas recovery assembly, wherein after sterilization the gas recovery assembly evacuates the sterilant gas mixture to the storage recovery tank. The system also includes an inert purge gas supply adapted to supply a purge gas to the sterilizer chamber after the sterilant gas mixture is withdrawn to the storage recovery tank, wherein the gas recovery assembly evacuates an additional portion of the purge gas from the sterilizer chamber to the storage tank to enrich the gas mixture for later reutilization in subsequent sterilization cycles.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 11/541,358 entitled “SYSTEM AND METHOD FORRECYCLING STERILANT GAS” filed by Douglas E. Bondar on Sep. 29, 2006,the entire disclosure of which is hereby incorporated by referenceherein.

BACKGROUND

1. Technical Field

The present disclosure relates to a system and method for recyclingsterilant gas. In particular, the present disclosure is directed torecovery and reuse of high concentration flammable sterilant gasmixtures, wherein the sterilant gas mixture is in concentrations greaterthan 20% by volume to a near an undiluted state of 100% by volume.

2. Discussion of Related Art

Ethylene oxide (“ETO”) is a sterilizing agent well known for itseffectiveness at certain gas concentrations. The objects which are to besterilized are placed in a hermitically sealed sterilization chamber andthe ETO vapor is pumped into the chamber. ETO gas is extremely flammableeven in the absence of air and is, therefore, used with extreme cautionin high concentrations at low pressures for sterilization purposes.Presently, high concentration ETO gas is not recycled and is only usedonce, afterwards the gas is then discharged to an emission controldevice for destruction.

One method for reusing ETO gas involves the use of a low concentrationmixture of ETO and an inert gas at higher process pressures. Highprocess pressures (e.g., up to 4 atmospheres) allow an increase in theETO gas concentration to an acceptable milligram per liter value foreffective sterilization. Mixtures having ratios of ETO to inert gas of10/90 and 20/80 are generally used. These mixtures contain sufficientETO concentration to assure sterilization regardless of the materialbeing sterilized under normal temperature and at above atmosphericpressure conditions. Relative non-flammability of diluted ETO and inertgas mixtures allows for recycling of these mixtures. However, thesemixtures are not as effective as higher concentrations of ETO gas.

The concentration of ETO decreases with continual use during thesterilization process since ETO is consumed in reaction with bacteria,water vapor, alcohol and the like during the sterilization process. Itis possible for the ETO gas concentration to be consumed to anunsatisfactory concentration for consistent sterilization effect.Therefore, low concentration gas mixtures require processing usinghigher pressure rated vessels, which are more expensive. This processalso involves processing the gases at above atmospheric pressures and,therefore, carries the risk of fugitive and catastrophic leakage.Consequently, in the industry today, all large ETO sterilizer chambersare designed to operate using low pressure and high concentration ETOgas. Existing sterilizers in use in the industry are not rated for thehigher pressures that are required to recycle low concentration ETO gassterilants.

It is desirable to provide a system and method for recycling sterilantgas mixtures having near 100% concentration of ETO gas to obtain maximumsterilization effectiveness while minimizing the complexity of theprocess and the cost of the sterilization equipment. It is desirable toprovide a system that can be retrofitted to existing sterilizationfacilities, by the utilization of the existing sterilization processequipment and avoiding the expenses that are associated with completesystem replacement.

SUMMARY

The present disclosure relates to a system and method for recycling highconcentration ethylene oxide (“ETO”) gas mixtures used in industrialsterilization processes. The system includes a sterilizer chamber ingaseous communication with a storage tank and a gas recovery assembly(e.g., vacuum draw). The gas recovery assembly withdraws the ETO gas tothe storage tank which is adapted to store the sterilant gas at apressure lower than the atmospheric pressure to minimize flammabilitythereof and fugitive leakage from the system. The ETO gas is stored inthe storage tank until the sterilization chamber is to be charged withthe ETO gas. It is envisioned that the storage tank may be replaced witha second sterilization chamber to allow for in tandem sterilizations. Athird or forth sterilization chamber may also be connected to the systemto allow gas transfer of the ETO gas from one sterilization chamber tothe next chamber, thereby continually utilizing recycled gas in eachsterilizer charge.

According to one embodiment of the present disclosure, a system forrecovery of sterilant gas from a sterilizer chamber is disclosed. Thesystem requires the use of an initial sterilizer evacuation and dilutionwith an inert purge gas to eliminate the air from the sterilizerchamber. The system includes a storage tank in gaseous communicationwith a sterilizer chamber via a gas recovery assembly, wherein gas canbe evacuated in either direction between the sterilizer chamber and thegas storage tank utilizing the recovery system. The system utilizes aninert purge gas to dilute the residual ETO gas remaining in thesterilizer chamber to a safe nonflammable concentration, after thesterilant gas is evacuated to the storage tank. The gas recoveryassembly evacuates additional diluted gas from the sterilizer chamber tothe storage tank to further increase the quantity of sterilant gas beingrecycled.

According to another embodiment of the present disclosure a method forrecovery of sterilant gas from a sterilizer chamber is disclosed. Themethod includes the steps of: evacuating a sterilant gas aftersterilization from a sterilizer chamber via a gas recovery assembly to astorage tank. An inert purge gas is added to the sterilizer chamberafter the sterilant gas charge is withdrawn to the storage tank toreduce the flammability of the sterilant gas. Some of the purge gas iswithdrawn from the sterilizer chamber and directed to the storage tankto be utilized in the enrichment of the gas mixture in the storage tank.

According to an embodiment of the present disclosure, a system forrecovery of sterilant gas mixture from a sterilizer chamber isdisclosed. The system includes a first sterilizer chamber in gaseouscommunication with a second sterilizer chamber via a gas recoveryassembly. After sterilization of the first sterilizer chamber, the gasrecovery assembly evacuates the sterilant gas mixture to the secondsterilizer chamber, where the mixture enriched with 100% ETO to apredetermined gas concentration to sterilize objects in the secondsterilizer chamber. The system also supplies an inert gas to the secondsterilizer chamber after the sterilant gas mixture has been evacuated tothe second sterilizer chamber, wherein the gas recovery assemblywithdraws the purge gas from the first sterilizer chamber to the secondsterilizer chamber to be utilized as additional replacement gas for thesterilant gas mixture in the second sterilizer chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1 is a schematic view of one embodiment of a sterilant gasrecycling system according to the present disclosure;

FIG. 2 is a schematic view of another embodiment of a sterilant gasrecycling system according to the present disclosure;

FIG. 3 is a schematic view of another embodiment of a sterilant gasrecycling system according to the present disclosure; and

FIG. 4 is a flow diagram of a method for recycling sterilant gasaccording to the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings. In the followingdescription, well-known functions or constructions are not described indetail to avoid obscuring the present disclosure in unnecessary detail.

Referring now to FIG. 1, a recycling system 2 in accordance with theprinciples of the present disclosure is illustrated. The recyclingsystem 2 is adapted to recapture and reuse a sterilant gas, such asethylene oxide (“ETO”). Those skilled in the art will appreciate thatthe present disclosure is not limited to recycling of ETO and that othersuitable gases selected for their sterilization properties may be used.

The recycling system 2 includes a sterilizer chamber 4 which isconfigured to be hermetically sealed once objects in need ofsterilization are placed therein to prevent gaseous flow between thesterilizer chamber 4 and the outside. The sterilizer chamber 4 includesone or more gas inlets 6 connected to a gas supply line 8. The gassupply line 8 includes an ETO supply 10, a steam supply 12, a purge gassupply 14, and a filtered air supply 16. The gas supply line 8 alsoincludes pressure actuated shut-off valves 18 in communication withpiping leading to the gas inlets 6. Each of the supplies 10, 12, 14 and16 include a secondary pressure actuated shut-off valve 20 and a checkvalve 22 which allows for unidirectional flow of gasses into thesterilizer chamber 4.

The ETO supply 10 provides a direct source of ETO gas to the sterilizerchamber 4 for the initial supply of ETO gas prior to commencement ofrecycling process as well as for any refortification of the ETO gas. TheETO supply 10 includes a heat exchanger 24 that is used to convert(e.g., vaporize) the liquid 100% ETO from the supply drums (notexplicitly shown) to vapor state. The steam supply 12 provides watersteam in multi-stage sterilization processes. The purge gas supply 14provides a purge gas (e.g., nitrogen, carbon dioxide, etc.) to the ETOgas within the sterilizer chamber 4 to decrease the flammability of theETO gas and to purge any remnants of the ETO gas after the first vacuumdraw as discussed in more detail below. The air supply 16 includes anair vent 26 and provides a supply of filtered air which is used to fillthe sterilizer chamber 4 after the ETO gas has been withdrawn to returnthe sterilizer chamber 4 to normal atmospheric conditions.

The recycling system 2 also includes a gas recovery assembly 28 which isin gaseous communication with the sterilizer chamber 4 and a recoverystorage tank 30. The gas recovery assembly 28 transfers the ETO gas fromthe sterilizer chamber 4 into the recovery tank 30. The gas recoveryassembly 28 includes a vacuum pump 32 and a circulation blower 34. Thepump 32 is connected to a plurality of pressure controlled shut offvalves 36 which control the direction of the gas flow through the gasrecovery assembly 28. In addition, the gas recovery assembly 28 includesa manual control valve 38 which allows to terminate gas flow therein(e.g., emergency situations). The circulation blower 34 can beconfigured to facilitate gas flow out of the sterilizer chamber 4 byfunctioning as a vacuum booster blower in series prior to the vacuumpump 32, to effect a deeper recovery vacuum from the sterilizer chamber,which will maximize the quantity of sterilant gas recovered.

Piping connecting the recovery tank 30 to the gas recovery assembly 28includes a pressure controlled shut-off valve 39. The recovery tank 30also includes a purge gas supply 40 and an ETO supply 42. Each of thesupplies 40 and 42 include a pressure controlled shut-off valve 44 and acheck valve 46. Further, the ETO supply 42 includes a heat exchanger 48to vaporize liquid ETO. The purge and ETO gas supplies 40 and 42 providethe storage tank 30 with nitrogen and ETO gases respectively such thatthe ratio of the gases can be adjusted during the recycling process.

Since the sterilant gas being used is high concentration ETO gas, thesterilization is accomplished at approximately atmospheric pressure tominimize flammability of the gas. It is also envisioned that thesterilizer chamber 4 and the storage tank 30 as well as other componentsof the recycling system 2 are rated for operation with flammable gasmixtures. During operation, the ETO gas is mixed with the purge gas indesired concentrations in the recovery tank 30 through the purge and ETOgas supplies 40 and 42 to form a sterilant gas mixture. Once objects areloaded into the sterilizer chamber 4, the chamber 4 is evacuated toremove air. Purge gas is added to the sterilizer chamber 4 through thepurge gas supply 14 and the sterilizer chamber 4 is again evacuated.This may be repeated a few times to ensure that all air is removed fromthe sterilizer chamber 4. Thereafter, the sterilant gas mixture ispumped into the sterilizer chamber 4 along with pure ETO gas and purgegas to achieve the desired gas ratio. The circulation blower 34 isactivated to mix the gases within the sterilant chamber 4.

After the sterilant gas mixture has been in the sterilizer chamber 4 fora sufficient amount of time to sterilize its contents, the vacuum pump32 evacuates the sterilizer chamber 4 and transfers to gas mixture backto the recovery tank 30. As the sterilant gas mixture is transferred,the pressure within the sterilizer chamber 4 is lowered to substantiallyvacuum conditions given structural limitations of the sterilizer chamber4 and capacity of the vacuum pump 32. The recovery tank 30 has a largervolume than the sterilizer chamber 4 (e.g., 110% of the volume of thesterilizer chamber 4) such that the pressure of transferred ETO gastherein is lower than the pressure of the gas within the sterilizerchamber 4 (i.e., atmospheric pressure). Since throughout thesterilization process all gases are stored and handled at pressureswhich are less than atmospheric, the environmental risk of fugitive gasleakage is drastically reduced.

After the recovery vacuum draw has been completed, the pressure in thesterilizer chamber 4 is increased to approximately 3 PSI by adding apurge gas (e.g., nitrogen gas) from the purge gas supply 14. A secondstage recovery vacuum draw is performed to recover gas from thesterilizer chamber 4 until the recovery tank 30 has achieved the targetpressure capacity, thereby mixing the ETO gas with the purge gas. Thesterilizer chamber 4 is then pressurized to atmospheric pressure usingpurge gas from the purge gas supply 14 or air from the filtered airsupply 16, if the contents of the sterilizer chamber 4 arenon-flammable. Thereafter, subsequent vacuum draws via the vacuum pump32 are discharged to standard emission control equipment (notspecifically shown) through a discharge vent 47.

The air is purged by the initial vacuum draws and displaced with inertdilution gas so that the percentage of air in the gas mixture does notexceed 20%. If the sum of the ETO percentage and the inert dilution gasis less than 80%, then gas is vented off to the emission control deviceand replaced with pure 100% dilution gas.

The ETO gas mixture is stored in the recovery tank 30 at atmosphericpressure and is transferred back to the sterilizer chamber 4 during thenext sterilization cycle via the vacuum pump 32. Prior to starting asterilization process cycle, the sterilant gas mixture in the recoverytank is sampled and analyzed using a process gas analyzer 49. Theanalyzer 49 can be installed at a port of a pressure vessel (e.g.,recovery tank 30, sterilizer chamber 4, etc.) or can be connected tomultiple vessels through a valve network of tubing. The analyzer 49 canutilize gas chromatography, or infrared spectral analysis, to obtainreliable measurements of the ETO gas and the purge gas amounts. It isdesirable to know the percentages of the gas components to ensureprocess safety. More specifically, concentration of gas componentsallows for calculation of the flammability of the process gas mixtureand sterilization effect on the objects in the sterilizer chamber 4.

The sterilization process according to the present disclosure isconfigured to operate via variety of validated ETO gas concentrations.The gas concentration is measured in the sterilizer chamber 4 during thesterilization gas exposure dwell. The pressure is then be adjustedaccording to the ideal gas law to control the gas density that theobjects being sterilized are exposed. Additional ETO gas is providedthrough the ETO gas supply 10 if the gas mixture within the sterilizerchamber 4 needs to be refortified. It is envisioned that ETO gasrecovery is about 85% of the original charge, wherein about 15% of theETO gas is lost due to product absorption, glycol conversion, vacuumpull down limitations, etc.

Referring to FIG. 2, another embodiment of the recycling system 2 isillustrated, wherein the storage tank 30 is replaced with a secondsterilizer chamber 50 which is in gaseous communication with the firststerilizer chamber 4. The sterilizer chamber 50 is configured to behermetically sealed and includes similar components as the sterilizerchamber 4. In particular, the sterilizer chamber 50 includes one or moregas inlets 52 connected to a gas supply line 54 which includes an ETOgas supply 56, a steam supply 58, a purge gas supply 60, and a filteredair supply 62. Each of the supplies 56, 58, 60 and 62 include asecondary pressure actuated shut-off valve 64 and a check valve 68 whichallows for unidirectional flow of gasses into the sterilizer chamber 50.

The gas recovery assembly 28 transfers the ETO gas between thesterilizer chamber 4 and the sterilizer chamber 50. The gas recoveryassembly 28 includes the vacuum pump 32, the circulation blower 34, asecond vacuum pump 70 and the circulation blower 72. The pumps 32 and 70are connected to a plurality of pressure controlled shut off valves 36which control the direction of the gas flow through the gas recoveryassembly 28. The circulation blowers 34 and 72 are configured tofacilitate gas flow between the sterilizer chambers 4 and 50.

During operation, the ETO gas is mixed with the purge gas in desiredconcentrations in the sterilizer chamber 50 through the ETO and purgegas supplies 56 and 60 to form a sterilant gas mixture. Once objects areloaded into the sterilizer chamber 4, one or more vacuum draws areperformed using purge gas to fill the sterilizer chamber 4. Thereafter,the sterilant gas mixture is pumped into the sterilizer chamber 4 alongwith pure ETO gas and purge gas to achieve the desired gas ratio. Thecirculation blower 34 is activated to mix the gases within the sterilantchamber 4.

After the sterilant gas mixture has been in the sterilizer chamber 4 fora sufficient amount of time to sterilize its contents, the vacuum pump32 evacuates the sterilizer chamber 4 and transfers to gas mixture backto the sterilizer chamber 50. As the ETO gas is transferred, thepressure within the sterilizer chamber 4 is lowered to substantiallyvacuum conditions given structural limitations of the sterilizer chamber4 and capacity of the vacuum pump 32. The sterilizer chamber 50 has asubstantially same volume as the sterilizer chamber 4 such that thepressure of transferred ETO gas therein is the same as the pressure ofthe gas within the sterilizer chamber 4 (i.e., atmospheric pressure).

After the recovery vacuum draw has been completed, the pressure in thesterilizer chamber 4 is increased to approximately 3 PSI by adding apurge gas (e.g., nitrogen gas) from the purge gas supply 14. A secondstage recovery vacuum draw is performed to recover gas from thesterilizer chamber 4 until the sterilizer chamber 50 has achieved thetarget pressure capacity, thereby mixing the ETO gas with the purge gas.The sterilizer chamber 4 is then pressurized to atmospheric pressureusing purge gas from the purge gas supply 14 or air from the filteredair supply 16, if the contents of the sterilizer chamber 4 arenon-flammable. Thereafter, subsequent vacuum draws via the vacuum pump32 are discharged to standard emission control equipment (notspecifically shown) through the discharge vent 47.

Additional ETO gas is provided to the sterilizer chamber 50 through theETO gas supply 56 if the gas mixture within the sterilizer chamber 50needs to be refortified. A heat exchanger 74 vaporizes liquid ETO intogaseous state. The recovered ETO gas mixture is kept within thesterilizer chamber 50 at atmospheric pressure and is transferred back tothe sterilizer chamber 4 during the next sterilization cycle once thesterilizer chamber 4 is prepared for another sterilization load.

Those skilled in the art will appreciate that multiple sterilizationchambers may be connected to each other to facilitate in tandemsterilization, thereby recycling the ETO gas by transferring the gasfrom one chamber or storage tank to another. FIG. 3 shows a furthermodification of three sterilizer chambers 4, 50 and 80 connected intandem as a single recovery system. The sterilant gas mixture istransferred from one sterilizer chamber to the next during thesterilization process. The sterilizer chamber 80 is connected to arecovery system 80 which is in gaseous communication with a recoverysystem 59 of the sterilizer chamber 50 and the recovery system 28 of thesterilizer chamber 4. Those skilled in the art will readily appreciatethat the recovery systems 4, 59 and 80 and the sterilizer chambers 4, 50and 80 include similar components as discussed above with embodimentsshown in FIGS. 1-2 (e.g., vacuum pumps, filtered air, nitrogen, steamand ETO gas supplies, etc.). This arrangement is desirable when objectsto be sterilized need to spend extended periods of time in thesterilizer chambers, e.g., for humidification and temperature warmingprior to gas exposure, extended product off-gassing time in the chamber,etc. The use of three or four sterilizer chambers operating in astaggered manner may also be desirable to sterilize certain dense typesof product.

FIG. 4 shows a flow chart of a method for recycling sterilant gasaccording to the present disclosure. In step 100, ETO gas and purge gasare mixed in desired proportions to form a sterilant gas mixture in therecovery tank 30 or a sterilizer chamber, if an in tandem system isbeing used. In step 110, concentration of the ETO and purge gases in thesterilant gas mixture is measured using the gas analyzer 49 to ensure asafe and effective sterilant gas composition. In step 120, enrichmentquantities for ETO and purge gases are calculated to ensure that theconcentration of ETO gas and pressure within the sterilizer chamber 4 isat a predetermined set point. In step 130, the sterilizer chamber 4 isevacuated and purged of air using one or more vacuum draws and adilution via purge gas. In step 140, undiluted ETO gas is added into thesterilizer chamber 4 to provide an initial charge of gas into thesterilizer based on the calculations of step 120.

In step 150, the sterilant gas mixture in the recovery tank 30 isevacuated into the sterilizer chamber 4. In step 160, the purge gas isadded to the sterilizer chamber 4 to raise the chamber pressure to nearatmospheric pressure to minimize the risk of air leaking into thechamber based on the calculations of step 120. In step 170, thecirculation blower 34 is activated to mix the gases added into thesterilization chamber. In step 180, concentration of ETO and purge gasesin the sterilant chamber 4 is measured. In step 190, ETO gas sterilityexposure gas concentration (e.g., milligrams per liter) is calculated.In step 200, the gas mixture is circulated and is maintained at apredetermined temperature and pressure within the sterilizer chamber 4.The sterilant gas mixture is kept in the sterilizer chamber 4 for asufficient amount of time, at validated temperature and predeterminedconcentration parameters to sterilize its contents. In step 210, thesterilizer chamber 4 is evacuated to transfer the sterilant gas mixtureback to the recovery tank 30 to pressurize the recovery tank 30 at ornear the atmospheric pressure. After the recovery vacuum draw has beencompleted, in step 220, purge gas (e.g., nitrogen gas) from the purgegas supply 14 is added to the sterilizer chamber 4. This increases thepressure in the sterilizer chamber 4 to approximately 3 PSI. In step230, a second stage recovery vacuum draw is performed to recover gasfrom the sterilizer chamber 4 until the sterilizer chamber 50 or thestorage tank 30 has achieved the target pressure capacity. In step 240,once the recovery tank 30 is at the desired pressure set point, thecontents of the sterilizer chamber 4 are evacuated to the emissioncontrol system. In step 250, the sterilizer chamber 4 is pressurized toatmospheric pressure using purge gas from the purge gas supply 14 or airfrom the filtered air supply 16. Optionally, subsequent vacuum draws aredischarged to standard emission control equipment through the dischargevent 47. In step 260, the mixture of ETO gas and the purge gas is storedin the recovery tank 30 or the sterilization chamber 50. The recoveredETO gas mixture is kept within the recovery tank 30 or the sterilizerchamber 50 at near atmospheric pressure and is transferred back to thesterilizer chamber 4 during the next sterilization cycle once thesterilizer chamber 4 is prepared for another sterilization load.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

1. A method for recovery of a sterilant gas mixture from a sterilizerchamber, comprising: withdrawing a sterilant gas mixture aftersterilization from a sterilizer chamber via a gas recovery assembly to astorage tank such that the pressure of the sterilant gas mixture islowered; supplying a purge gas to the sterilizer chamber after thesterilant gas mixture is withdrawn to the storage tank; and withdrawingthe purge gas from the sterilizer chamber to the storage tank to form acombined mixture of the sterilant gas mixture and the purge gas.
 2. Amethod according to claim 1, wherein the storage tank has a volumehigher than a volume of the sterilizer chamber and wherein, during thestep of withdrawing the sterilant gas mixture, the storage tank isadapted to store the sterilant gas mixture at pressure lower than theatmospheric pressure.
 3. A method according to claim 1, wherein thepurge gas is an inert gas and wherein during the step of withdrawing thepurge gas, the inert gas is withdrawn from the sterilizer chamber to thestorage tank to form a combined mixture of the sterilant gas mixture andthe inert gas.
 4. A method according to claim 1, further comprising:evacuating the storage tank prior to withdrawing the sterilant gasmixture from the sterilizer chamber.
 5. A method according to claim 1,wherein supplying the purge gas further includes supplying the purge gasto the sterilizer chamber to pressurize the sterilizer chamber at apressure lower than atmospheric pressure.
 6. A method according to claim1, further comprising: pressurizing the sterilizer chamber atatmospheric pressure after the purge gas is withdrawn from thesterilizer chamber to the storage tank.
 7. A method according to claim1, wherein the purge gas is an inert gas and wherein while withdrawingthe purge gas, the inert gas is withdrawn from the sterilizer chamber tothe storage tank to form a combined mixture of the sterilant gas mixtureand the inert gas.
 8. A method for recovery of a sterilant gas mixturefrom a sterilizer chamber, comprising: withdrawing a sterilant gasmixture after sterilization from a sterilizer chamber via a gas recoveryassembly to a storage tank such that the pressure of the sterilant gasmixture is lowered; supplying a purge gas to the sterilizer chamberafter the sterilant gas mixture is withdrawn to the storage tank;withdrawing the purge gas from the sterilizer chamber to the storagetank to form a combined mixture of the sterilant gas mixture and thepurge gas; and supplying the combined mixture of the sterilant gasmixture and the purge gas to the sterilizer chamber.
 9. A methodaccording to claim 8, wherein the storage tank has a volume higher thana volume of the sterilizer chamber, and wherein while withdrawing thesterilant gas mixture, the storage tank is adapted to store thesterilant gas mixture at pressure lower than atmospheric pressure.
 10. Amethod according to claim 8, wherein the purge gas is an inert gas andwherein while withdrawing the purge gas, the inert gas is withdrawn fromthe sterilizer chamber to the storage tank to form a mixture of thesterilant gas mixture and the inert gas.
 11. A method according to claim8, further comprising the step of: evacuating the storage tank prior towithdrawing the sterilant gas mixture from the sterilizer chamber.
 12. Amethod according to claim 8, wherein the step of supplying the purge gasfurther includes supplying the purge gas to the sterilizer chamber topressurize the sterilizer chamber at a pressure lower than atmosphericpressure.
 13. A method according to claim 8, further comprising the stepof: pressurizing the sterilizer chamber at atmospheric pressure afterthe purge gas is withdrawn from the sterilizer chamber to the storagetank.
 14. A method according to claim 8, wherein the step of withdrawingthe purge gas from the sterilizer chamber further includes storing thecombined mixture of the sterilant gas mixture and the purge gas atatmospheric pressure within the storage tank.
 15. A method for recoveryof a sterilant gas mixture from a sterilizer chamber, comprising:withdrawing a sterilant gas mixture after sterilization from asterilizer chamber via a gas recovery assembly to a storage tank suchthat the pressure of the sterilant gas mixture is lowered; supplying apurge gas to the sterilizer chamber after the sterilant gas mixture iswithdrawn to the storage tank; withdrawing the purge gas from thesterilizer chamber to the storage tank to form a combined mixture of thesterilant gas mixture and the purge gas; supplying the combined mixtureof the sterilant gas mixture and the purge gas to the sterilizerchamber; determining an amount of at least one of the sterilant gasmixture and the purge gas present in the combined mixture; andrefortifying the combined mixture with at least one of the sterilant gasmixture and the purge gas based on the determined amount in the combinedmixture.
 16. A method according to claim 15, wherein the storage tankhas a volume higher than a volume of the sterilizer chamber, and whereinwhile withdrawing the sterilant gas mixture, the storage tank is adaptedto store the sterilant gas mixture at a pressure lower than atmosphericpressure.
 17. A method according to claim 15, wherein the purge gas isan inert gas and wherein while withdrawing the purge gas, the inert gasis withdrawn from the sterilizer chamber to the storage tank to form acombined mixture of the sterilant gas mixture and the inert gas.
 18. Amethod according to claim 15, further comprising: evacuating the storagetank prior to withdrawing the sterilant gas mixture from the sterilizerchamber.
 19. A method according to claim 15, wherein supplying the purgegas further includes supplying the purge gas to the sterilizer chamberto pressurize the sterilizer chamber at a pressure lower thanatmospheric pressure.
 20. A method according to claim 15, furthercomprising: pressurizing the sterilizer chamber at atmospheric pressureafter the purge gas is withdrawn from the sterilizer chamber to thestorage tank.
 21. A method according to claim 15, wherein withdrawingthe purge gas from the sterilizer chamber further includes storing thecombined mixture of the sterilant gas mixture and the purge gas atatmospheric pressure within the storage tank.